The present invention relates to an apparatus for feeding powderized raw material, such as aluminum oxide, into an aluminum producing electrolysis comprising an anode and cathode apparatus, and means for transferring powderized raw material from a silo or equivalent to the feeding apparatus. The raw material is fed by means of the feeding apparatus into an electrolyte melt in which electrolysis occurs. Electrolysis is the process of producing a chemical change by the passage of an electric current through an electrolyte, e.g., an electrolyte cell or other non-metallic electric conductor in which current is carried, such that the ions present carry the current by migrating to the electrodes. A method for feeding powderized raw material into an aluminum producing electrolysis reaction is also disclosed.
The invention is classified within an electrolytic production range of aluminum accomplished in an electrolysis reaction with self-baking anodes. However, the present invention can be used in electrolysis reactions provided with baked anodes, and in which the electrolysis cells are fed with aluminum oxide or other equivalent raw materials.
In the prior art, the electrolysis process of the production of aluminum is accomplished as a continuous process. The feeding of the raw material, preferably aluminum oxide, is usually carried out intermittently in the form of batch feeding by penetrating the crust of electrolyte, and in practice, by feeding an uncontrolled portion of aluminum oxide spread prior to transmission of the raw material upon the crust.
In prior art feeding methods utilizing various feeding means, major failures occur in the electrolysis process which can cause instability in the process. This is primarily due to the fact that the concentration of aluminum oxide in the molten electrolyte changes from the maximum value at the charging moment to a minimum value at the starting moment of an anode effect. As a result, the consumption of electrical energy increases, the efficiency of the current decreases and precipitations are formed on the bottom of the electrolysis cell.
Other significant problems related to electrolytic aluminum production include the problem of guaranteeing a reliable and simple continuous feeding of the electrolysis reaction without substantially breaking the electrolyte crust so that a sufficiently uniform aluminum oxide concentration can be maintained in the electrolysis reaction.
Among the prior art techniques, U.S.S.R. Inventor's Certificate No. SU 126,217 describes a method for feeding aluminum oxide into an aluminum producing electrolysis reaction wherein aluminum oxide is fed into the electrolyte using a vibration method. The purpose of this method is to accelerate the dissolution of aluminum oxide in the electrolyte cell and to prevent precipitation thereof on the bottom of the electrolyte cell. According to the SU inventor's certificate, the aluminum oxide travels from a silo through a dispenser along a pipe to a feeding means vibrating with the aid of a vibratory drive means.
In a first alternative embodiment of this prior art device, the feeding means is a spherical pump provided with apertures for discharging the aluminum oxide. By vibrating the feeding means, which has an amplitude directed in a horizontal direction, the purpose of the spherical pump immersed within the electrolytic electrolyte cell is to assist in dissolving the aluminum oxide in the electrolyte. According to a second alternative embodiment, a horizontal plate is attached to a vibrator such that a tip of the plate is immersed within the electrolyte. When subjected to the vibration forces, the aluminum oxide passes from the plate into the electrolyte cell in order to intensify the dissolution process of aluminum oxide.
This prior art process is not used conventionally in view of the fact that there are difficulties associated with maintaining the surface of the molten electrolyte cell open at the aluminum oxide feeding point. This is because the crust is produced rapidly on the surface of the molten electrolyte when cold aluminum oxide enters into contact with the electrolyte. Additional difficulties are caused by the fact that there are no materials which are capable of resisting the cryolite-aluminum oxide melt.
U.S. Pat. No. 2,713,024 describes a prior art method for the continuous feeding of an aluminum producing electrolysis reaction wherein a pipe is placed under a feeding means positioned on the surface of the electrolyte melt. Aluminum oxide is fed into the pipe and conveyed to an aluminum oxide column produced in the melt at the inlet area with pressure being provided by the feeding means. The feeding means which provide the pressure are not in contact with the aluminum oxide column being directed into the melt. The process according to this prior art device is, independent on the electrolysis, accomplished with feeding means including a silo, below which is located a dispenser unit of screw type and a conveying pipe connecting the dispenser with the feeding means. In the feeding means, diverse screw, piston or crank lever mechanisms are used which change the rotary motion of the flywheel into an advancing circulatory motion and which have been mounted on the feeding pipe on the surface of the electrolyte melt, and connected with electrically operating means.
The device of U.S. Pat. No. 2,713,024 requires the use of a means with which aluminum oxide is carried into the melt with the aid of the energy of pressurized air. The feeders of the aluminum oxide can be mounted, depending on the type of electrolysis, on the side of, inside of or in the middle of the anodes. In spite of the advantages of the process described in this prior art device, it has not come into a wider use because a significant drawback of this device is that when the raw material is introduced into the molten electrolyte through the electrolyte crust, difficulties have arisen in overcoming the large forces produced therein.